1. Field of the Invention
The invention relates generally to the art of air-ride axle/suspension systems for heavy-duty vehicles, such as tractor-trailers or semi-trailers, which cushion the ride and stabilize the vehicle during operation. More specifically, the invention relates to control of the air springs of an air-ride axle/suspension system, and in particular to a pneumatic proportioning system which regulates and proportions air among air springs of an air-ride axle/suspension system.
2. Background Art
Heavy-duty vehicles, such as tractor-trailers or semi-trailers, typically include two or more leading or trailing arm suspension assemblies that connect the wheel-bearing axles of the vehicle to the frame of the vehicle. Early suspension designs included heavy leaf spring suspensions which resulted in a relatively rough ride to the cargo and/or passengers carried by the vehicle, and did not allow loads to equalize among the axles in all situations, thus creating the need for an axle/suspension system with softer ride characteristics and more efficient equalization characteristics. The subsequent development of air-ride axle/suspension systems provided greater load equalization among multiple axles for semi-trailers as well as improved ride quality for individual axles.
As a result, heavy-duty vehicles that transport freight often include leading or trailing arm air-ride axle/suspension systems, which use air springs to cushion the ride of the vehicle. Pneumatic control of these air springs is an important feature of air-ride axle/suspension systems.
More particularly, it is important for a cushioned vehicle ride, and for optimum axle/suspension system performance and longevity, to attempt to maintain a consistent, predetermined distance between the vehicle frame and the travel surface. This predetermined distance is known in the art as the design ride height of the vehicle. The operating conditions of the vehicle must be considered in order to establish the design ride height of a vehicle. That is, when a heavy-duty vehicle executes certain maneuvers, such as making a hard turn or traveling over rough terrain, the forces imposed on the axle/suspension system by such maneuvers cause the axle/suspension system to articulate, or pivot and/or flex beneath the vehicle frame which the system supports. Typically, an axle/suspension system is designed so that the anticipated range of articulation, pivoting and/or flexing occurs about a nominal predetermined position, and that nominal position is set as the design ride height of the vehicle.
After a heavy-duty vehicle is loaded with freight, or after freight is unloaded from the vehicle, the air springs of the axle/suspension system are adjusted to ensure that the vehicle is at design ride height. The adjustment of the air springs of the axle/suspension system is typically accomplished by a height control valve or leveling valve which is in fluid communication with an air source and with the air springs. When the vehicle is loaded with freight and the air springs of an axle/suspension system are compressed causing the vehicle frame to be positioned below design ride height or closer to the travel surface, compressed air is supplied to the air springs increasing the air pressure inside the air spring, thereby increasing air spring load. The increasing air spring load inflates/extends the air springs in turn causing the axle/suspension system to raise the vehicle frame to the design ride height. Conversely, when the vehicle is unloaded and the air springs of the axle/suspension system are extended causing the vehicle frame to be positioned above design ride height or further away from the travel surface, air is exhausted from the air springs reducing the internal pressure, thereby deflating/compressing them until the axle/suspension system lowers the vehicle frame to the design ride height. As set forth above, the adjustment of the air springs, including regulation of air flow into the air springs and the exhaustion of air from the air springs, is controlled by a mechanically operated valve known in the art as a height control valve. Adjustments to the height control valve and the linkage that controls activation of the valve enable the design ride height to be achieved.
As the vehicle travels over the road and the driver executes maneuvers that cause the axle/suspension system to articulate between a position that compresses the air springs and a position that extends them, the height control valve automatically acts to maintain the design ride height. That is, when the air springs are compressed, the height control valve causes air to be supplied to the air springs from a vehicle air reservoir. Conversely, when the air springs are in an extended position, the height control valve causes air to be exhausted from the air springs to atmosphere. The amount of air that is supplied or exhausted to and from, respectively, the air springs, is based on the duration of the articulation of the suspension beam and the flow rate of the height control valve at a given position.
Subsequent prior art pneumatic control systems have included a solenoid valve which is incorporated into the pneumatic control system that allows the operator of the vehicle to “dump” or exhaust the air springs of the rear axle/suspension system in order to increase maneuverability of the vehicle. The solenoid valve typically is in fluid communication with the conduit disposed between the height control valve and the rear air springs. The solenoid valve is utilized to exhaust the air springs of the suspension assemblies of the rear axle/suspension system when the vehicle operator encounters a situation that requires increased maneuverability of the heavy-duty vehicle. More particularly, the solenoid valve is electrically connected to a control switch that is located in the cab of the heavy-duty vehicle. When the operator desires to exhaust the air springs of the rear axle/suspension system of the vehicle in order to increase maneuverability, the operator engages a switch that sends an electrical supply or impulse to the solenoid valve. Once energized, the solenoid value prohibits the flow of air from the height control valve to the air springs of the rear axle/suspension system and, instead, allows fluid or air in the air springs of the rear axle/suspension system to flow through the solenoid valve to atmosphere. Typically, these prior art pneumatic control systems exhaust all of the air from the air springs of the rear axle/suspension system. By exhausting all of the air in the air springs of the rear axle/suspension system, the trailer longitudinal wheel-base is effectively shortened, as the cargo loads which had previously been imparted approximately equally on both the front and rear axle/suspension systems are shifted forward to the front axle/suspension system of the trailer.
This effective shortening of the longitudinal wheel base of the heavy-duty vehicle as a result of complete exhaustion of the air springs of the rear axle/suspension system increases maneuverability of the vehicle, but may lead to premature failure of certain components of the front and rear axle/suspension systems. Problems which can typically occur in these prior art pneumatic control systems that exhaust all of the air from the air springs of the rear axle/suspension system include: 1) overloading of the front axle/suspension system and its associated components; 2) contact between the jounce stop or bumper of the air spring and the upper bead plate of the air spring in both the front and rear axle/suspension systems; and 3) trapping of the exhausted air springs of the rear axle/suspension system. More particularly, when the air is exhausted as described above in a vehicle which is heavily loaded, the front axle/suspension system to which the cargo loads are effectively transferred can become overloaded, which can lead to premature failure of the front axle/suspension system and its associated components, such as the axle, the suspension assemblies, the air springs, the wheel end assemblies, and the tires.
Also, when the air is exhausted as described above in a vehicle which is heavily loaded, the front axle/suspension system to which the cargo loads are effectively transferred is often unable to maintain vehicle ride height. More specifically, the loads that are transferred to the front axle/suspension system may require a pressure in the air springs that far exceeds the available system pressure. When this occurs, the vehicle height drops until the jounce stop or bumper in each air spring of the front and rear suspension assemblies of the axle/suspension systems contacts the upper bead plate of the air spring. The result being that the vehicle is no longer air suspended. In this state, forces due to road inputs such as bumps or pot-holes, are directly transmitted to the vehicle frame at much higher levels as the bumper stiffness is significantly higher than that of the air spring at design ride height. Such uncontrolled load transfer can exceed the maximum design strength of the air spring jounce stop and the suspension assembly components, possibly causing these components to fail prematurely. In addition, when the jounce stop or bumper in each air spring of the axle/suspension system contacts the upper bead plate, the friction between the jounce stop or bumper and the upper bead plate may greatly reduce the ability of the suspension assemblies to move in a horizontal plane. The movement of the suspension assemblies in a horizontal plane as a result of lateral forces is commonly referred to as lateral compliance steer. The reduction in lateral compliance steer can increase the magnitude of the lateral forces acting on the suspension assemblies when the vehicle makes a turn. Increased lateral forces acting through the suspension assemblies also increase the probability of premature failure of the components of the suspension assemblies. Yet another common issue which is prevalent in current prior art pneumatic control systems is the tendency for the flexible air spring member of the exhausted air spring to pinch or become trapped at the top of the air spring piston. This trapping occurs when the air springs are completely exhausted during a suspension assembly dump, i.e., when the air springs of the rear suspension assembly are exhausted completely. This trapping of the flexible air spring member can increase the probability of premature failure of the air spring. More specifically, the flexible member of the air spring becomes trapped between the internal jounce stop and the upper bead plate of the air spring which can cause damage to the flexible member.
Therefore, a need exists in the art for a pneumatic control system for the air springs of an air-ride axle/suspension system of a heavy-duty vehicle, which overcomes the deficiencies of prior art pneumatic control systems by proportioning air between the suspension assemblies of the axle/suspension systems, such as between the front and rear air springs, side to side, or diagonally, in order to prevent overloading of the axle/suspension systems and to minimize contact between the jounce stop or bumper of the air springs and the upper bead plates of the air springs. Such overloading and undesirable contact can cause the air springs and the suspension assembly components of an axle/suspension system to exceed maximum design strength and increases the probability of premature failure of the axle/suspension systems and their associated components, in addition to decreasing lateral steer compliance of the suspension assemblies which can increase the probability of premature failure of the components. Moreover, minimizing contact between the jounce stop or bumper of the air spring and the upper bead plate of the air spring can prevent pinching or trapping of the flexible member of the air spring, which can minimize the possibility of premature failure of the air spring.